A mysterious rebound in the emissions of ozone-depleting chemicals – despite a global ban stretching back almost a decade – has been traced to eastern China.

Research published by an international team today in Nature used a global network of monitoring stations to pinpoint the source of the rogue emissions. According to these data, 40-60% of the increase in emissions seen since 2013 is due to possibly illegal industrial activity in the Chinese provinces of Shandong and Hebei.

Chlorofluorocarbon-11 (CFC-11) is a powerful ozone-depleting chemical that plays a major role in the appearance, each spring, of the ozone “hole” over Antarctica.

In the past, CFC-11 had been used primarily as a propellant in aerosol products and as a foam plastic blowing agent. The production and consumption (use) of CFC-11 are controlled by the global Montreal Protocol. CFC-11 consumption has been banned in developed countries since 1996, and worldwide since 2010.

This has resulted in a significant decline of CFC-11 in the atmosphere. Long-term CFC-11 measurements at Cape Grim, Tasmania, show the amount in the atmosphere peaked in 1994, and fell 14% by 2018.

However, this decline has not been as rapid as expected under the global zero production and consumption mandated by the Montreal Protocol since 2010.

Background levels of CFC-11 measured at Australia’s Cape Grim Baseline Air Pollution Station, located at the north-west tip of Tasmania.CSIRO/Bureau of Meteorology

A 2014 study was the first to deduce that global emissions of CFC-11 stopped declining in 2002. In 2015, CSIRO scientists advised the Australian government, based on measurements compiled by the Advanced Global Atmospheric Gases Experiment (AGAGE), which includes those from Cape Grim, that emissions had risen significantly since 2011. The cause of this rebound in CFC-11 emissions was a mystery.

Global CFC-11 emissions based on atmospheric measurements compared with the expected decline of this compound in the atmosphere if compliance with the Montreal Protocol was adhered to.CSIRO/AGAGE

Montzka’s team concluded that if these increased CFC-11 emissions continued, the closure of the Antarctic ozone hole could be delayed, possibly for decades. This was a remarkable piece of detective work, considering that Mauna Loa is more than 8,000km from East Asia.

Suspicions confirmed

A still more detailed explanation is published today in the journal Nature by an international research team led by Matt Rigby of the University of Bristol, UK, and Sunyoung Park of Kyungpook National University, South Korea, together with colleagues from Japan, the United States, Australia and Switzerland. The new study uses data collected every two hours by the AGAGE global monitoring network, including data from Gosan, South Korea, and from an AGAGE-affiliated station at Hateruma, Japan. Crucially, Gosan and Hateruma are just 1,000km and 2,000km, respectively, from the suspected epicentre of CFC-11 emissions in East Asia.

The Korean and Japanese data show that these new emissions of CFC-11 do indeed come from eastern China – in particular the provinces of Shandong and Hebei – and that they have increased by around 7,000 tonnes per year since 2013.

Meanwhile, the rest of the AGAGE network has detected no evidence of increasing CFC-11 emissions elsewhere around the world, including in North America, Europe, Japan, Korea or Australia.

Yet while this new study has accounted for roughly half of the recent global emissions rise, it is possible that smaller increases have also taken place in other countries, or even in other parts of China, not covered by the AGAGE network. There are large swathes of the globe for which we have very little detailed information on CFC emissions.

Map showing the region where the increased CFC-11 emissions came from, based on atmospheric measurements and modelling.University of Bristol/CSIRO

Nevertheless, this study represents an important milestone in atmospheric scientists’ ability to tell which regions are emitting ozone-depleting substances and in what quantities. It is now vital we find out which industries are responsible for these new emissions.

If the emissions are due to the manufacture and use of products such as foams, it is possible that, so far, we have seen in the atmosphere only a fraction of the total amount of CFC-11 that was produced illegally. The remainder could be locked up in buildings and chillers, and will ultimately be released to the atmosphere over the coming decades.

This study highlights the importance of undertaking long-term measurements of trace gases like CFC-11 to verify that international treaties and protocols are working. It also identifies shortcomings in the global networks for detecting regional emissions of ozone depleting substances. This should encourage expansion of these vital measurement networks which would lead to a capability of more rapid identification of future emission transgressions.

The headlines in recent months read like an international eco-thriller.

At Mauna Loa Observatory, perched high on a Hawaiian volcano, researchers measure unusual levels of CFC-11 in the atmosphere. The measurements baffle the scientific community: CFC-11, a potent ozone-depleting gas, has been carefully monitored since it was banned under the 1987 Montreal Protocol. But the measurements are soon confirmed by observing stations in Greenland, American Samoa and Antarctica. The evidence points to illegal production of the banned chemical, threatening the fragile recovery of Earth’s UV-shielding ozone layer. But the identity of the environmental super-villain remains a mystery.

Then, a breakthrough. By running global climate models backwards, a team of scientists in Boulder, Colorado, trace the source of CFC-11 to East Asia. The trail is picked up by the Environmental Investigation Agency, a tiny activist organisation based above a coffee shop in Islington, London. EIA dispatches investigators to China and uncovers rampant illegal production of CFC-11 for insulation foam used in the Chinese construction industry. “This is an environmental crime on a massive scale,” says Clare Perry, EIA’s climate campaign leader.

Meanwhile, scientists and diplomats from around the world converge on Vienna for a meeting of the United Nations working group on the Montreal Protocol. EIA’s blockbuster report is high on the agenda. But can the international community band together once more to protect the ozone layer and save “the world’s most successful environmental treaty”?

A model of cooperation

The last time the ozone hole was front-page news, President Ronald Reagan was still eating jelly beans in the Oval Office. In 1985 British scientists announced the discovery of a shocking decline in atmospheric ozone concentrations high above Antarctica. The “ozone hole”, as it became known, was caused by ozone-eating chemicals called chlorofluorocarbons (CFCs) used as refrigerants in air conditioners and propellants in aerosol spray cans.

The discovery galvanised public opinion, particularly over concerns about the risk of skin cancer, cataracts and sunburn associated with increased exposure to ultraviolet radiation. In Australia and New Zealand, popular ad campaigns featuring a dancing seagull encouraged the beach-goers to “Slip on a shirt, slop on sunscreen, and slap on a hat!”.

In his signing statement, Reagan heralded the Montreal Protocol as “a model of cooperation” and “a product of the recognition and international consensus that ozone depletion is a global problem”. It remains his signature environmental achievement.

An enduring impact on Earth’s climate

Three decades after Montreal, the ozone layer is showing signs of recovery. In January 2018, a NASA study found that the ozone hole was the smallest it had been since 1988, the year before the Montreal protocol went into effect. But a full recovery will take decades. “CFCs have lifetimes from 50 to 100 years, so they linger in the atmosphere for a very long time,” said NASA scientist Anne Douglass, one of the authors of the study. “As far as the ozone hole being gone, we’re looking at 2060 or 2080.”

In the meantime, CFCs continue to impact Earth’s climate in some unexpected ways. CFCs are powerful greenhouse gases, with more than 5,000 times the warming potential of an equivalent weight of carbon dioxide. It is estimated that banning CFCs and other ozone-depleting chemicals has delayed global warming by as much as a decade.

However, those gains are threatened by the ozone-friendly, but heat-trapping, chemicals that have replaced CFCs in our air conditioners and insulation. The latest amendment to the Montreal Protocol will phase out the use of this new class of chemicals by 2028.

Even more surprising is the complex influence of the ozone hole on Earth’s atmosphere and oceans. The loss of UV-absorbing ozone over the South Pole has changed the pattern of winds around Antarctica. Strengthened winds blowing over the Southern Ocean draw more deep water towards the surface, where it is “ventilated” by contact with the atmosphere.

Deep Antarctic water is rich in carbon, making it a poor absorber of atmospheric CO₂. That means that the ocean has become less efficient at removing excess carbon dioxide from the atmosphere, reducing its ability to offset global warming.

Darryn Waugh on the ozone threat.

Lessons from a world avoided

The success of the Montreal Protocol holds lessons for today’s efforts to confront human-induced climate change. Vigorous leadership by Reagan and the then British prime minister, Margaret Thatcher, a trained chemist, was crucial during the negotiations of the treaty. The protocol began modestly and was designed to be flexible so that more ozone-depleting substances could be phased out by later amendments. Developing countries were also provided with incentives and institutional support to meet their compliance targets.

Lessons from the World Avoided: Dr Sean Davis at TEDx Boulder 2017.

But perhaps the most important lesson is the need for action, even when the science is not yet conclusive. “We don’t need absolute certainty to act,” says Sean Davis, a climate scientist at the US National Oceanic and Atmospheric Administration. “When Montreal was signed, we were less certain then of the risks of CFCs than we are now of the risks of greenhouse gas emissions.”

Professor Darryn Waugh will present a public lecture about the enduring impact of the ozone hole on climate at UNSW Sydney on July 30, 2018. Details and registration information are available here.

Editor’s note: Curbing damage to Earth’s protective ozone layer is widely viewed as one of the most important successes of the modern environmental era. Earlier this year, however, a study reported that ozone concentrations in the lower level of the stratosphere had been falling since the late 1990s – even though the Montreal Protocol, a global treaty to phase out ozone-depleting chemicals, had been in effect since 1989. This raised questions about whether and how human activities could still be damaging the ozone layer. Atmospheric chemist A.R. Ravishankara, who co-chaired a United Nations/World Meteorological Organization Scientific Assessment panel on stratospheric ozone from 2007 to 2015, provides perspective.

What’s the prevailing view among atmospheric scientists today about the state of the ozone layer?

The overall picture is clear: The Montreal Protocol reduced use of ozone-depleting chemicals and will lead to healing of the ozone layer. This is an important goal because stratospheric ozone protects us from exposure to ultraviolet radiation, which can increase the risk of cataracts, skin cancer and other detrimental effects.

Of course, this forecast would be wrong if nations deviate from their treaty commitments, or if the scientific community fails to detect possible emissions of gases that could deplete the ozone layer but are not covered by the treaty.

The ozone layer in the stratosphere shields life on Earth from most UV-B and UV-C, the most harmful varieties of ultraviolet radiation.NASA

Our understanding of stratospheric ozone depletion has grown steadily since the mid-1970s, when Mario Molina and F. Sherwood Rowland first suggested that the ozone layer could be depleted by chlorofluorocarbons, or CFCs – research that earned a Nobel Prize. In 1985 Joseph Farman reported on the formation of an “ozone hole” – actually, a large-scale thinning of the ozone layer – that develops over Antarctica every austral spring.

Further work by Susan Solomon and colleagues clearly attributed the ozone hole to CFCs and other ozone-depleting chemicals that contained the elements chlorine and bromine. They also highlighted unusual reactions that take place on polar stratospheric clouds.

In 1987, the United States and 45 other countries signed the Montreal Protocol, which required them to phase out use of ozone-depleting substances. Today 197 nations have ratified the treaty, which has prevented large-scale ozone layer depletion and its harmful consequences. Ozone-depleting substances are also greenhouse gases that trap heat in the atmosphere, so phasing them out under the Montreal Protocol has also helped to slow climate change.

It takes decades to cleanse CFCs and other ozone depleting substances from the atmosphere, so even after the Montreal Protocol went into effect, their concentrations did not peak until around 1998 and are still high. Nonetheless, based on atmospheric observations, laboratory studies of chemical reactions and numerical models of the stratosphere, there is general consensus among scientists that the ozone layer is on track to recover around 2060, give or take a decade. We also know that the future of the ozone layer is intricately intertwined with climate change.

Ozone is constantly created and destroyed in Earth’s atmosphere as oxygen interacts with ultraviolet light, but man-made chemicals can disrupt this process.

What could explain the continued decline in ozone in the lower stratosphere that was reported earlier this year?

Of course, there are still some gaps in our knowledge of the ozone layer, and these two new reports have spotlighted such gaps.

The first study reported that although ozone concentrations were increasing in the upper stratosphere, they were still declining in the lower stratosphere. It suggested several possible causes, such as increases in uncontrolled, very short-lived gases produced from human activities that can deplete the ozone layer, as well as changes in atmospheric circulation due to climate change.

The second study identified rising levels of certain chlorinated chemicals, referred to as very short-lived substances, that could continue to deplete the ozone layer.

These reports were a little surprising, but not shocking. Scientists expect that we will continue to add to our knowledge of ozone layer, and our understanding will emerge as we digest these findings. The Montreal Protocol requires the scientific community to carry out scientific assessments of ozone depletion every four years precisely because we expect that new information like this will continue to emerge. One of those reviews is under way now and will be published later this year.

If industrial activities causing this decline in the lower stratosphere, Montreal Protocol member countries can amend the treaty to address these new threats. They did so in 2016 to phase out hydrofluorocarbons – coolants, used in air conditioners and refrigerators, that were found to be powerful greenhouse gases.

U.S. Secretary of State John Kerry delivers a speech to delegates from Montreal Protocol member countries in Kigali, Rwanda, Oct. 14, 2016. At the meeting nations agreed on a deal to phase out hydrofluorocarbons from air conditioners and refrigerators.AP Photo

If ozone levels in the lower stratosphere have been decreasing for 20 years, why are scientists just detecting that trend now?

Ozone levels change naturally from year to year, so scientists need to look at data over long time periods to tease out trends. The potential for short-lived chlorine and bromine gases to affect the ozone layer has been recognized for a while. More recently, scientists have been measuring concentrations in the atmosphere of dichloromethane, a liquid that is widely used as a solvent, and deduced that if it continues to increase, it will be a potential problem. Trends in emissions of these compounds are uncertain, but some recent results suggest that they are not increasing as rapidly as they appeared to be a few years ago.

Did these studies find any changes in the ozone hole?

No, they did not. They examined ozone changes within 60 degrees of the equator, not over the Antarctic. We do not expect very short-lived substance emissions to significantly influence the ozone hole unless they increase drastically, but this is one more reason to keep an eye on them.

Do these recent findings make you question whether the Montreal Protocol is effective?

No! Indeed, they strengthen my trust in it.

With any environmental agreement, whether it addresses ozone depletion, acid rain, climate change or other issues, it is important to be vigilant during the “accountability phase” – the period after policy decisions have been made and before the targeted results are expected. I am confident that if scientific findings warrant it, Montreal Protocol countries will take further action, and that my granddaughters will see the day when we eliminate the ozone hole.

On October 28, Australia ratified the Kigali Amendment to the Montreal Protocol. Australia is the tenth country to ratify, joining others as diverse as Mali, the United Kingdom and Rwanda in a global commitment to dramatically reduce hydrofluorocarbons (HFCs) in the atmosphere. Once 20 countries have ratified the amendment, it will become binding.

HFCs were designed specifically to replace ozone-destroying compounds previously used in air conditioners and refrigerants. Unfortunately, we now know that HFCs are massively potent greenhouse gases – thousands of times more powerful than carbon dioxide (albeit released in far smaller quantities).

If the Kigali Amendment becomes binding, the hunt will begin for a replacement for HFCs and their uses in industry. In a strange twist, the least environmentally harmful option may well be carbon dioxide.

Where do HFCs come from?

HFCs are made of carbon, fluorine and hydrogen. They are exclusively synthetic, meaning they have no known natural sources. To understand why they came into existence requires a quick history lesson.

Throughout the second half of the 20th century, another class of compounds called chlorofluorocarbons (CFCs) were widely used. CFCs are very stable, which made them ideal for many practical uses, including in refrigeration, foam packaging, and even aerosol cans for hair spray.

The Montreal Protocol was a global agreement developed to stop this harmful ozone destruction. The protocol mandated a time frame to completely abolish CFCs. To replace them, new compounds were developed that do not destroy ozone: HFCs.

The usage of CFCs and their replacements, including HFCs, since 1950.UNEP 2011. HFCs: A Critical Link in Protecting Climate and the Ozone Layer

But the solution to one environmental problem became the cause of another: these replacements are potent contributors to warming the climate.

Why are HFCs so bad?

All greenhouse gases work by absorbing infrared radiation, which would otherwise escape into space. But not all greenhouse gases are created equal. The potency of a greenhouse gas depends on three properties:

how long it remains in the atmosphere (its “lifetime”)

how much radiation it absorbs

whether the specific wavelength of radiation it absorbs would otherwise be absorbed by something else in the atmosphere (like water).

Combined, these three properties can be used to determine the global warming potential for each greenhouse gas. This is a measure of how potent the gas is relative to carbon dioxide (CO₂). By definition, CO₂ has a global warming potential of 1. Methane, commonly considered the second most important greenhouse gas, has a global warming potential of 34 – meaning that 1 tonne of methane would trap 34 times more heat than 1 tonne of CO₂.

The global warming potentials for the three most abundant HFCs range from 1,370 to 4,180. In other words, these gases trap thousands of times more heat in our atmosphere than an equivalent amount of CO₂.

What will replace HFCs?

The nearly 200 countries that signed the original Montreal Protocol have unanimously agreed that the climate risks posed by HFCs are too significant to ignore. Developed countries will begin phasing out HFCs in 2019. Developing countries will follow suit between 2024 and 2028.

So what will our refrigerators and air conditioners use instead? Several replacements are being considered.

Another option is to use mixtures of hydrocarbons such as butane. Hydrocarbons pose safety risks as they are highly flammable and may also adversely affect air quality. Ammonia is another alternative that has been used as a refrigerant for a long time but is highly toxic.

And, finally, there is the surprise candidate: CO₂. Although using CO₂ as a refrigerant poses technical challenges, it is non-toxic and non-flammable and a much weaker greenhouse gas than the HFCs it would replace. Strangely, from an environmental perspective, CO₂ may actually be the “best” refrigerant available.

A cooler future ahead?

The Montreal Protocol has long been considered one of the greatest environmental success stories of all time. It brought together the world’s governments and chemical industries to protect the ozone layer.

The adoption of the Kigali Amendment will be another feather in the cap of this important agreement. HFCs aren’t overly prevalent yet – but without Kigali they are expected to grow rapidly. By banning them now, we will avoid their impacts before it is too late.

This weekend marks the 30th birthday of the Montreal Protocol, often dubbed the world’s most successful environmental agreement. The treaty, signed on September 16, 1987, is slowly but surely reversing the damage caused to the ozone layer by industrial gases such as chlorofluorocarbons (CFCs).

Each year, during the southern spring, a hole appears in the ozone layer above Antarctica. This is due to the extremely cold temperatures in the winter stratosphere (above 10km altitude) that allow byproducts of CFCs and related gases to be converted into forms that destroy ozone when the sunlight returns in spring.

As ozone-destroying gases are phased out, the annual ozone hole is generally getting smaller – a rare success story for international environmentalism.

Back in 2012, our Saving the Ozone series marked the Montreal Protocol’s silver jubilee and reflected on its success. But how has the ozone hole fared in the five years since?

It typically takes a few decades for these gases to cycle between the lower atmosphere and the stratosphere, and then ultimately to disappear. The most recent official assessment, released in 2014, predicted that it will take 30-40 years for the Antarctic ozone hole to shrink to the size it was in 1980.

Signs of recovery

Monitoring the ozone hole’s gradual recovery is made more complicated by variations in atmospheric temperatures and winds, and the amount of microscopic particles called aerosols in the stratosphere. In any given year these can make the ozone hole bigger or smaller than we might expect purely on the basis of halocarbon concentrations.

Launching an ozone-measuring balloon from Australia’s Davis Research Station in Antarctica.Barry Becker/BOM/AAD, Author provided

The 2014 assessment indicated that the size of the ozone hole varied more during the 2000s than during the 1990s. While this might suggest it has become harder to detect the healing effects of the Montreal Protocol, we can nevertheless tease out recent ozone trends with the help of sophisticated atmospheric chemistry models.

Reassuringly, a recent study showed that the size of the ozone hole each September has shrunk overall since the turn of the century, and that more than half of this shrinking trend is consistent with reductions in ozone-depleting substances. However, another study warns that careful analysis is needed to account for a variety of natural factors that could confound our detection of ozone recovery.

Average ozone concentrations over the southern hemisphere during October 1-15, 2015, when the Antarctic ozone hole for that year was near its maximum extent. The red line shows the boundary of the ozone hole.Paul Krummel/CSIRO/EOS, Author provided

Another notable feature of the 2015 ozone hole was that it was at its biggest observed extent for much of the period from mid-October to mid-December. This coincided with a period during which the jet of westerly winds in the Antarctic stratosphere was particularly unaffected by the warmer, more ozone-rich air at lower latitudes. In a typical year, the influx of air from lower latitudes helps to limit the size of the ozone hole in spring and early summer.

The 2017 hole

As noted above, the ozone holes of 2013, 2014 and 2016 were relatively unremarkable compared with that of 2015, being close to the long-term average for overall ozone loss.

In general respects, these ozone holes were similar to those seen in the late 1980s and early 1990s, before the peak of ozone depletion. This is consistent with a gradual recovery of the ozone layer as levels of ozone-depleting substances gradually decline.

This year’s hole began to form in early August, and the timing was similar to the long-term average. Stratospheric temperatures during the Antarctic winter were slightly cooler than in 2016, which would favour enhancement of the chemical changes that lead to ozone destruction in spring. However, temperatures climbed above average in mid-August during a disturbance to the polar winds, delaying the hole’s expansion. As of the second week of September, the warmer-than-average temperatures have continued but the ozone hole has grown slightly larger than the long-term average since 1979.

While annual monitoring continues, which includes measurements under the Australian Antarctic Program, a more comprehensive assessment of the ozone layer’s prospects is set to arrive late next year. Scientists across the globe, coordinated by the UN Environment Program and the World Meteorological Organisation, are busy preparing the next report required under the Montreal Protocol, called the Scientific Assessment of Ozone Depletion: 2018.

This peer-reviewed report will examine the recent state of the ozone layer and the atmospheric concentration of ozone-depleting chemicals, how the ozone layer is projected to change, and links between ozone change and climate.

In the meantime we’ll watch the 2017 hole as it peaks then shrinks over the remainder of the year, as well as the ozone holes of future years, which will tend to grow less and less large as the ozone layer heals.

The agreement ended a decade of negotiations under the Montreal Protocol, established in 1987 to protect the ozone layer. Under the new agreement, developed nations will reduce HFCs 85% below current levels by 2036.

So how will the deal work?

Fixing the ozone hole

The Montreal Protocol was established under the Vienna Convention for the protection of the ozone layer. It followed evidence that chlorine atoms were damaging the stratospheric ozone, which protects the Earth from the most energetic ultraviolet radiation coming from the sun.

These chlorine atoms came from refrigerant and propellant gases, the chlorofluorocarbons (CFCs), that we were releasing into the atmosphere.

By 1990, nations had agreed to restrict production and consumption of CFCs and a timetable for their eventual phase-out over the next two decades. More time was allowed for developing countries and a multilateral fund was established to help them meet their targets.

With just a few exceptions, complete phase-out has been achieved. As well as ozone protection, there was a climate benefit from phasing-out the CFCs because they are much stronger greenhouse gases than carbon dioxide.

Related gases that were less damaging to the ozone layer, the hydrochlorofluorocarbons (HCFCs), were next targeted and they will have been phased out by about 2020.

In developed countries such as Australia they have largely disappeared already, although there is still a lot of one HCFC, R-22, in older air-conditioners. Other ozone-depleting substances such as the fumigant methyl bromide and a number of solvents were also targeted for elimination under the Montreal Protocol.

New villain

Major replacements for the CFCs were the hydrofluorocarbons (HFCs). Their molecules contain no chlorine so they are “ozone friendly” but like the CFCs these substances are serious global warmers.

HFCs are not manufactured in Australia but we import several thousand tonnes each year, which is a small proportion of world production. Our imports will be capped from 2018 following a recent government decision.

Nations under the Montreal Protocol realised that by using HFCs to replace ozone-depleting substances they had contributed to another environmental problem – global warming and climate change.

Despairing of any action under the climate change-centred Kyoto Protocol, the representatives of developed countries began to push for addition of HFCs to the Montreal Protocol where production and consumption data could be monitored and there was potential for an agreement to phase them out.

The process was fractious. Some parties argued that the Montreal Protocol could not be extended to cover substances that were not ozone-depleting. Others pointed to a clause in the preamble to the protocol that would allow HFCs to be covered.

This was a practical view, but perhaps it also contained an element of guilt: “we created the problem so it’s up to us to fix it”.

Resistance came from developing countries that were struggling financially to achieve the phase-out of HCFCs and did not want the expense of retooling for whatever would replace the HFCs.

In the corridors one could hear cynical voices saying that the phase-outs of CFCs and HCFCs would leave delegates and officers with nothing to do, so an extension to HFCs was needed to keep the “Montreal Club” alive.

Send in the replacements

Sensing that change was likely, the chemical industry in the US had already produced HFC replacements that are neither ozone-depleting nor global warming – the hydrofluoroolefins (HFOs).

These substances are designed to rapidly degrade in the lower atmosphere so that releases would not contribute to environmental problems. Other industrial players, strongly backed by environment groups, opted for natural refrigerants such as ammonia (already coming into widespread use in Australia), carbon dioxide (yes, the villain in new clothes!), and low-boiling hydrocarbons such as isobutane that can be “dropped in” to air-conditioners to replace the HFC R-134a.

Last week in Kigali, countries agreed to a phase-out schedule they could live with. Reductions will occur in steps: developed countries have until 2036 to reduce HFC consumption to 85% of current levels, while developing countries have until the mid-2040s. This is too slow for some observers but the experience of the last decade’s negotiations showed that measured pace would be important in securing the agreement.

Australian delegates had been involved all along in the group pushing for the extension of the Montreal Protocol to cover the HFCs. More than that, our lead delegate, Patrick McInerney (Department of the Environment) was co-chair of the working group that fashioned the Kigali consensus and enabled the 197 parties to bring the matter to conclusion.

Even the most pedantic observer, while questioning the validity of extending the Montreal Protocol, would have to agree that it was the right thing to do.

Remember when the world came together to save the ozone layer — even Ronald Reagan and Margaret Thatcher? The Montreal Protocol, a treaty that went into effect in 1989, curbed the use of CFCs and other chemicals that tear up the planet’s UV-absorbing sheath of ozone. But that was nearly a generation ago — and things still haven’t been fully patched up in the lower stratosphere.

The ongoing fragility of the ozone layer reminds us how long it can take for atmospheric conditions to stabilize after we have screwed them up. The L.A. Times reports:

In 2006, the ozone hole grew larger than ever. It reached a similar extent in 2011, before shrinking to its second-smallest size in 2012. Naturally occurring meteorological conditions were mostly responsible for those fluctuations, two NASA studies found.

Over the next two decades scientists expect the ozone hole to continue to vary widely.